1. Field of the Invention
The present invention relates to an engine having an auxiliary cylinder and a valve slidable in this cylinder. The invention also relates to a method for operating the engine.
2. Description of the Related Art
FIG. 24 shows the variable compression ratio engine disclosed in JP 2005-30235 A. The connecting rod 13 of this engine includes an upper part 16 and a lower part 17, which are connected by a joint 18. The joint 18 is connected to a control rod 21. The engine has a mechanism for shifting the control rod 21 to vary the distance between the ends of the connecting rod 13. Combustion gas pressure is exerted on the joint 18 and the shifting mechanism. This pressure is high when the piston is under a heavy load. This causes problems with the durability of the joint 18 and the shifting mechanism.
FIG. 25 shows an engine in which combustion gas pressure is exerted on the movable member 4 in the auxiliary chamber. FIG. 26 shows an engine in which combustion gas pressure is exerted on the auxiliary piston 9. In each of these engines, the mechanism for changing the volume of the combustion chamber moves against the combustion gas pressure. This causes a problem with the durability of the changing mechanism.
FIG. 27 shows the engine shown in FIG. 3.248 on page 237 of “History of Internal Combustion Engines” published by San-ei Shobo of Shinjuku, Tokyo. The piston of this engine reciprocates in a double sleeve. The cylinder head of this engine has outer peripheral grooves, in which piston rings are fitted. The piston rings are in contact with the inner cylindrical surface of the double sleeve. If overhead poppet valves were fitted inside the double sleeve, the peripheral grooves would restrict the area where the valves could be fitted. This would decrease the suction efficiency and exhaust efficiency of the poppet valves.
The suction resistance and exhaust resistance of a four cycle engine are high when it rotates at high speed. The suction lifts in this engine are extremely small in the initial stages of the periods when the suction valve is open. The initial stages are shorter when the engine rotates at a higher speed. This restricts the inflow of suction gas. As a result, in the initial stages of the periods when the suction valve is open, the pressure in the cylinder is lower than the pressure at the back of the piston. Under this condition, the piston keeps moving downward against the pressure on it. As a result, the negative work increases. This increases the loss caused by the suction resistance, so that the torque lowers.
FIG. 28 shows the engine performance curves shown on page 90 of No. 434 issued in November, 1995 of a magazine entitled “Internal Combustion Engine” published by Sankaido. With reference to FIG. 28, the torque of a four cycle engine is lower than the maximum torque points L1 and L2 on torque curves when the engines rotate at speeds higher than those for these points.
The exhaust lifts in a four cycle engine are extremely smaller in the initial stage of the period when the exhaust valve is open until the piston reaches the bottom dead point of each exhaust stroke than in the middle stage of this period. Consequently, when the engine rotates at high speed, the pressure created in the cylinder when the piston is at the bottom dead point is high. As a result, just after the piston leaves the bottom dead point, the exhaust resistance causes a great loss.
FIG. 29 shows the side valve engine disclosed in JP 2000-282814 A. The main combustion chamber 54 of this engine has an extension outside the cylinder. This makes it possible to fit another suction valve and another exhaust valve that face the top of the piston. The space between the suction and exhaust valves is narrowed to make the combustion chamber compact.
However, the volume of the main combustion chamber 54 is increased by the space between the wall fitted with a side valve and the surface facing the wall. The volume of this space increases with the lift of the side valve. Consequently, the combustion chamber having a suction valve facing the top of the piston and a side valve cannot have a high combustion ratio, so that the engine efficiency is low.
If the strokes of the piston are longer than its diameter, the combustion gas conversion efficiency is high, but the suction efficiency is low when the engine rotates at high speed. The low suction efficiency leads to low torque. If the piston strokes are shorter than the piston diameter, the suction efficiency is high when the engine rotates at high speed, but the combustion gas conversion efficiency is low.
Therefore, long strokes of the pistons of conventional spark ignition engines have been incompatible with torque increases that may be caused when the engines rotate at high speed.